We have noticed that since about upgrade to tha latest WordPress (or rather "since 6-8 weeks"), Flexi-Pages introduces a severe performance problem: when FP is active, a page-load goes from 4-5 sec (page weighs in at ~1.6MB) to 35-180 seconds. And that not being all, publishing often takes 5-6 MINUTES and then often gives a 403 and the tags are not acknowledged ...
I tested all plugins we use, one after the other, and this was the one alone slowed the website down.
We are on a shared hoster, using PHP 5.3.21 amd MySQL 5.3 iirc.
I have opted to deactivate FP for now, what makes the website look :-(
Thanks for your consideration and kind regards.